The Statistical Development Core (SDC) will refine and develop appropriate statistical methods directly relevant to the demographic studies being conducted in the first four research projects. Each of these research projects includes detailed plans for specific statistical analyses of the data collected. The investigators in the SDC will develop methodological innovations to analyze the data in alternative ways. The thrust of this research will be to more fully exploit the data to deepen and extend substantive research findings on patterns of oldest-old mortality. To facilitate this substantively-focused methodological research, the SDC will coordinate a biweekly research seminar for consultation and interchange among the statisticians collaborating on this program project, including the six senior statistical investigators, the data base manager, and various PH.D students in Statistics and Biometry who will be involved as research assistants. Funding for three statistical investigators (Louis, Smith and Zelterman) is requested in this core: funding for the others is included in specific projects. Louis will provide overall leadership as Principal Investigator, will lead research efforts to develop new methods to handle heterogeneity in univariate and multivariate survival analysis and to develop semi-parametric and consistent modeling methods, and will take primary responsibility for coordination with project 2 on Danish Twins. Smith will focus on study designs for the Medfly and Drosophila experiments with emphasis on two-phase stratified sampling methods for coping with the non-sampling errors in the Swedish, Danish, and U.S. data sets, and will take primary responsibility for coordination with project 3 on Medflies. Zeltermans' special interest is extreme values and tail behavior in survival curves and he will work to develop methods to exploit the data gathered in the four projects on mortality patterns at the most advanced ages, including the data set on all Swedish centenarians born since 1720. He will take primary responsibility for coordination with project 1 on Swedish and U.S. mortality and project 4 on Drosophila.